html:-moz-full-screen {
    background: grey;
}

html:-webkit-full-screen {
    background: grey;
    width: 100%;
    height: 100%;
}

html:fullscreen {
    background: grey;
    width: 100% !important;
    height: 100% !important;
}

:not(:root):fullscreen::backdrop {
    background: whitesmoke;
}

.pear-full-screen {
    width: 100% !important;
    height: 100% !important;
}